1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly to a method for transmitting uplink data during handoff of a mobile station.
2. Description of the Related Art
FIG. 1 is a schematic block diagram illustrating the structure of a conventional cellular communication network. Generally, base transceiver systems (BTSs) 111 to 113 and a BTS 114, which provide radio interfaces to a mobile station, are connected to BTS controllers (BSCs) 121 and 122, respectively. The BSCs 121 and 122 are connected with each other in order to share control information between them, and these are connected to a core network 130 including an authentication, authorization, and accounting server and a home agent for security.
A mobile station performs handoff under the control of the BSCs in the network having the above-described structure and transmits the same data to BTSs connected to the mobile station while performing the handoff.
FIG. 2 is a view for explaining a method for transmitting uplink data when performing intra-BSC handoff in the conventional cellular communication network. A mobile station 10 transmits the same data signal to two BTSs 111 and 112 connected to the mobile station. The two BTSs 111 and 112 having received the data signal from the mobile station 10 decode the data signal. If the two BTSs 111 and 112 successfully decode the data signal, they transmit a cyclic redundancy check (CRC) value and data to the BSC 121. If the two BTSs 111 and 112 fail to decode the data signal, they transmit only a CRC value to the BSC 121.
FIG. 3 is a view for explaining a method for transmitting uplink data when performing inter-BSC handoff in the conventional cellular communication network. Each of the BTSs 111 and 112 demodulates a data signal received from the mobile station 110 and transmits the demodulated soft data bit string and corresponding channel information to the BSCs 121 and 122 connected to the BTSs 111 and 112, respectively. The BSCs 121 and 122 decode soft data bit strings received from the BTSs 111 and 112 by diversity-combining the soft data bit strings.
However, in the case of the intra-BSC handoff, it is difficult to obtain a sufficient amount of a decoding gain after diversity-combining soft data bit strings received through two different paths even though it is possible to obtain data having high reliability based on a CRC value.
In addition, in the case of the inter BSC handoff, although it is possible to obtain a sufficient amount of a decoding gain, since a vast amount of traffic due to the transmission of soft data bits between BTCs and BSCs is generated, a computation amount for decoding signals transmitted from a plurality of BTSs and a memory having a mass storage capacity for storing previously received signals due to a time delay to receive soft data bit strings from BTSs are required.